diff --git a/lib/parser.js b/lib/parser.js
index e7d8c0f..44548d9 100644
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -99,65 +99,55 @@ module.exports = (function() {
             },
         peg$c19 = "&",
         peg$c20 = { type: "literal", value: "&", description: "\"&\"" },
-        peg$c21 = function(code) {
-              return {
-                type: "semantic_and",
-                code: code
-              };
-            },
-        peg$c22 = function(expression) {
+        peg$c21 = function(expression) {
               return {
                 type:       "simple_and",
                 expression: expression
               };
             },
-        peg$c23 = "!",
-        peg$c24 = { type: "literal", value: "!", description: "\"!\"" },
-        peg$c25 = function(code) {
-              return {
-                type: "semantic_not",
-                code: code
-              };
-            },
-        peg$c26 = function(expression) {
+        peg$c22 = "!",
+        peg$c23 = { type: "literal", value: "!", description: "\"!\"" },
+        peg$c24 = function(expression) {
               return {
                 type:       "simple_not",
                 expression: expression
               };
             },
-        peg$c27 = "?",
-        peg$c28 = { type: "literal", value: "?", description: "\"?\"" },
-        peg$c29 = function(expression) {
+        peg$c25 = "?",
+        peg$c26 = { type: "literal", value: "?", description: "\"?\"" },
+        peg$c27 = function(expression) {
               return {
                 type:       "optional",
                 expression: expression
               };
             },
-        peg$c30 = "*",
-        peg$c31 = { type: "literal", value: "*", description: "\"*\"" },
-        peg$c32 = function(expression) {
+        peg$c28 = "*",
+        peg$c29 = { type: "literal", value: "*", description: "\"*\"" },
+        peg$c30 = function(expression) {
               return {
                 type:       "zero_or_more",
                 expression: expression
               };
             },
-        peg$c33 = "+",
-        peg$c34 = { type: "literal", value: "+", description: "\"+\"" },
-        peg$c35 = function(expression) {
+        peg$c31 = "+",
+        peg$c32 = { type: "literal", value: "+", description: "\"+\"" },
+        peg$c33 = function(expression) {
               return {
                 type:       "one_or_more",
                 expression: expression
               };
             },
-        peg$c36 = "(",
-        peg$c37 = { type: "literal", value: "(", description: "\"(\"" },
-        peg$c38 = ")",
-        peg$c39 = { type: "literal", value: ")", description: "\")\"" },
-        peg$c40 = function(expression) { return expression; },
-        peg$c41 = void 0,
-        peg$c42 = function(name) {
+        peg$c34 = "(",
+        peg$c35 = { type: "literal", value: "(", description: "\"(\"" },
+        peg$c36 = ")",
+        peg$c37 = { type: "literal", value: ")", description: "\")\"" },
+        peg$c38 = function(expression) { return expression; },
+        peg$c39 = void 0,
+        peg$c40 = function(name) {
               return { type: "rule_ref", name: name }
             },
+        peg$c41 = function(code) { return { type: "semantic_and", code: code }; },
+        peg$c42 = function(code) { return { type: "semantic_not", code: code }; },
         peg$c43 = { type: "any", description: "any character" },
         peg$c44 = { type: "other", description: "whitespace" },
         peg$c45 = "\t",
@@ -1017,7 +1007,7 @@ module.exports = (function() {
         if (s1 !== peg$FAILED) {
           s2 = peg$parse__();
           if (s2 !== peg$FAILED) {
-            s3 = peg$parseCodeBlock();
+            s3 = peg$parseSuffixedExpression();
             if (s3 !== peg$FAILED) {
               peg$reportedPos = s0;
               s1 = peg$c21(s3);
@@ -1036,12 +1026,12 @@ module.exports = (function() {
         }
         if (s0 === peg$FAILED) {
           s0 = peg$currPos;
-          if (input.charCodeAt(peg$currPos) === 38) {
-            s1 = peg$c19;
+          if (input.charCodeAt(peg$currPos) === 33) {
+            s1 = peg$c22;
             peg$currPos++;
           } else {
             s1 = peg$FAILED;
-            if (peg$silentFails === 0) { peg$fail(peg$c20); }
+            if (peg$silentFails === 0) { peg$fail(peg$c23); }
           }
           if (s1 !== peg$FAILED) {
             s2 = peg$parse__();
@@ -1049,7 +1039,7 @@ module.exports = (function() {
               s3 = peg$parseSuffixedExpression();
               if (s3 !== peg$FAILED) {
                 peg$reportedPos = s0;
-                s1 = peg$c22(s3);
+                s1 = peg$c24(s3);
                 s0 = s1;
               } else {
                 peg$currPos = s0;
@@ -1064,67 +1054,7 @@ module.exports = (function() {
             s0 = peg$c0;
           }
           if (s0 === peg$FAILED) {
-            s0 = peg$currPos;
-            if (input.charCodeAt(peg$currPos) === 33) {
-              s1 = peg$c23;
-              peg$currPos++;
-            } else {
-              s1 = peg$FAILED;
-              if (peg$silentFails === 0) { peg$fail(peg$c24); }
-            }
-            if (s1 !== peg$FAILED) {
-              s2 = peg$parse__();
-              if (s2 !== peg$FAILED) {
-                s3 = peg$parseCodeBlock();
-                if (s3 !== peg$FAILED) {
-                  peg$reportedPos = s0;
-                  s1 = peg$c25(s3);
-                  s0 = s1;
-                } else {
-                  peg$currPos = s0;
-                  s0 = peg$c0;
-                }
-              } else {
-                peg$currPos = s0;
-                s0 = peg$c0;
-              }
-            } else {
-              peg$currPos = s0;
-              s0 = peg$c0;
-            }
-            if (s0 === peg$FAILED) {
-              s0 = peg$currPos;
-              if (input.charCodeAt(peg$currPos) === 33) {
-                s1 = peg$c23;
-                peg$currPos++;
-              } else {
-                s1 = peg$FAILED;
-                if (peg$silentFails === 0) { peg$fail(peg$c24); }
-              }
-              if (s1 !== peg$FAILED) {
-                s2 = peg$parse__();
-                if (s2 !== peg$FAILED) {
-                  s3 = peg$parseSuffixedExpression();
-                  if (s3 !== peg$FAILED) {
-                    peg$reportedPos = s0;
-                    s1 = peg$c26(s3);
-                    s0 = s1;
-                  } else {
-                    peg$currPos = s0;
-                    s0 = peg$c0;
-                  }
-                } else {
-                  peg$currPos = s0;
-                  s0 = peg$c0;
-                }
-              } else {
-                peg$currPos = s0;
-                s0 = peg$c0;
-              }
-              if (s0 === peg$FAILED) {
-                s0 = peg$parseSuffixedExpression();
-              }
-            }
+            s0 = peg$parseSuffixedExpression();
           }
         }
       }
@@ -1141,15 +1071,15 @@ module.exports = (function() {
         s2 = peg$parse__();
         if (s2 !== peg$FAILED) {
           if (input.charCodeAt(peg$currPos) === 63) {
-            s3 = peg$c27;
+            s3 = peg$c25;
             peg$currPos++;
           } else {
             s3 = peg$FAILED;
-            if (peg$silentFails === 0) { peg$fail(peg$c28); }
+            if (peg$silentFails === 0) { peg$fail(peg$c26); }
           }
           if (s3 !== peg$FAILED) {
             peg$reportedPos = s0;
-            s1 = peg$c29(s1);
+            s1 = peg$c27(s1);
             s0 = s1;
           } else {
             peg$currPos = s0;
@@ -1170,15 +1100,15 @@ module.exports = (function() {
           s2 = peg$parse__();
           if (s2 !== peg$FAILED) {
             if (input.charCodeAt(peg$currPos) === 42) {
-              s3 = peg$c30;
+              s3 = peg$c28;
               peg$currPos++;
             } else {
               s3 = peg$FAILED;
-              if (peg$silentFails === 0) { peg$fail(peg$c31); }
+              if (peg$silentFails === 0) { peg$fail(peg$c29); }
             }
             if (s3 !== peg$FAILED) {
               peg$reportedPos = s0;
-              s1 = peg$c32(s1);
+              s1 = peg$c30(s1);
               s0 = s1;
             } else {
               peg$currPos = s0;
@@ -1199,15 +1129,15 @@ module.exports = (function() {
             s2 = peg$parse__();
             if (s2 !== peg$FAILED) {
               if (input.charCodeAt(peg$currPos) === 43) {
-                s3 = peg$c33;
+                s3 = peg$c31;
                 peg$currPos++;
               } else {
                 s3 = peg$FAILED;
-                if (peg$silentFails === 0) { peg$fail(peg$c34); }
+                if (peg$silentFails === 0) { peg$fail(peg$c32); }
               }
               if (s3 !== peg$FAILED) {
                 peg$reportedPos = s0;
-                s1 = peg$c35(s1);
+                s1 = peg$c33(s1);
                 s0 = s1;
               } else {
                 peg$currPos = s0;
@@ -1241,32 +1171,38 @@ module.exports = (function() {
           if (s0 === peg$FAILED) {
             s0 = peg$parseRuleReferenceExpression();
             if (s0 === peg$FAILED) {
-              s0 = peg$currPos;
-              if (input.charCodeAt(peg$currPos) === 40) {
-                s1 = peg$c36;
-                peg$currPos++;
-              } else {
-                s1 = peg$FAILED;
-                if (peg$silentFails === 0) { peg$fail(peg$c37); }
-              }
-              if (s1 !== peg$FAILED) {
-                s2 = peg$parse__();
-                if (s2 !== peg$FAILED) {
-                  s3 = peg$parseChoiceExpression();
-                  if (s3 !== peg$FAILED) {
-                    s4 = peg$parse__();
-                    if (s4 !== peg$FAILED) {
-                      if (input.charCodeAt(peg$currPos) === 41) {
-                        s5 = peg$c38;
-                        peg$currPos++;
-                      } else {
-                        s5 = peg$FAILED;
-                        if (peg$silentFails === 0) { peg$fail(peg$c39); }
-                      }
-                      if (s5 !== peg$FAILED) {
-                        peg$reportedPos = s0;
-                        s1 = peg$c40(s3);
-                        s0 = s1;
+              s0 = peg$parseSemanticPredicateExpression();
+              if (s0 === peg$FAILED) {
+                s0 = peg$currPos;
+                if (input.charCodeAt(peg$currPos) === 40) {
+                  s1 = peg$c34;
+                  peg$currPos++;
+                } else {
+                  s1 = peg$FAILED;
+                  if (peg$silentFails === 0) { peg$fail(peg$c35); }
+                }
+                if (s1 !== peg$FAILED) {
+                  s2 = peg$parse__();
+                  if (s2 !== peg$FAILED) {
+                    s3 = peg$parseChoiceExpression();
+                    if (s3 !== peg$FAILED) {
+                      s4 = peg$parse__();
+                      if (s4 !== peg$FAILED) {
+                        if (input.charCodeAt(peg$currPos) === 41) {
+                          s5 = peg$c36;
+                          peg$currPos++;
+                        } else {
+                          s5 = peg$FAILED;
+                          if (peg$silentFails === 0) { peg$fail(peg$c37); }
+                        }
+                        if (s5 !== peg$FAILED) {
+                          peg$reportedPos = s0;
+                          s1 = peg$c38(s3);
+                          s0 = s1;
+                        } else {
+                          peg$currPos = s0;
+                          s0 = peg$c0;
+                        }
                       } else {
                         peg$currPos = s0;
                         s0 = peg$c0;
@@ -1283,9 +1219,6 @@ module.exports = (function() {
                   peg$currPos = s0;
                   s0 = peg$c0;
                 }
-              } else {
-                peg$currPos = s0;
-                s0 = peg$c0;
               }
             }
           }
@@ -1349,14 +1282,14 @@ module.exports = (function() {
         }
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
         }
         if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
-          s1 = peg$c42(s1);
+          s1 = peg$c40(s1);
           s0 = s1;
         } else {
           peg$currPos = s0;
@@ -1370,6 +1303,71 @@ module.exports = (function() {
       return s0;
     }
 
+    function peg$parseSemanticPredicateExpression() {
+      var s0, s1, s2, s3;
+
+      s0 = peg$currPos;
+      if (input.charCodeAt(peg$currPos) === 38) {
+        s1 = peg$c19;
+        peg$currPos++;
+      } else {
+        s1 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$c20); }
+      }
+      if (s1 !== peg$FAILED) {
+        s2 = peg$parse__();
+        if (s2 !== peg$FAILED) {
+          s3 = peg$parseCodeBlock();
+          if (s3 !== peg$FAILED) {
+            peg$reportedPos = s0;
+            s1 = peg$c41(s3);
+            s0 = s1;
+          } else {
+            peg$currPos = s0;
+            s0 = peg$c0;
+          }
+        } else {
+          peg$currPos = s0;
+          s0 = peg$c0;
+        }
+      } else {
+        peg$currPos = s0;
+        s0 = peg$c0;
+      }
+      if (s0 === peg$FAILED) {
+        s0 = peg$currPos;
+        if (input.charCodeAt(peg$currPos) === 33) {
+          s1 = peg$c22;
+          peg$currPos++;
+        } else {
+          s1 = peg$FAILED;
+          if (peg$silentFails === 0) { peg$fail(peg$c23); }
+        }
+        if (s1 !== peg$FAILED) {
+          s2 = peg$parse__();
+          if (s2 !== peg$FAILED) {
+            s3 = peg$parseCodeBlock();
+            if (s3 !== peg$FAILED) {
+              peg$reportedPos = s0;
+              s1 = peg$c42(s3);
+              s0 = s1;
+            } else {
+              peg$currPos = s0;
+              s0 = peg$c0;
+            }
+          } else {
+            peg$currPos = s0;
+            s0 = peg$c0;
+          }
+        } else {
+          peg$currPos = s0;
+          s0 = peg$c0;
+        }
+      }
+
+      return s0;
+    }
+
     function peg$parseSourceCharacter() {
       var s0;
 
@@ -1564,7 +1562,7 @@ module.exports = (function() {
         }
         peg$silentFails--;
         if (s5 === peg$FAILED) {
-          s4 = peg$c41;
+          s4 = peg$c39;
         } else {
           peg$currPos = s4;
           s4 = peg$c0;
@@ -1596,7 +1594,7 @@ module.exports = (function() {
           }
           peg$silentFails--;
           if (s5 === peg$FAILED) {
-            s4 = peg$c41;
+            s4 = peg$c39;
           } else {
             peg$currPos = s4;
             s4 = peg$c0;
@@ -1670,7 +1668,7 @@ module.exports = (function() {
         }
         peg$silentFails--;
         if (s5 === peg$FAILED) {
-          s4 = peg$c41;
+          s4 = peg$c39;
         } else {
           peg$currPos = s4;
           s4 = peg$c0;
@@ -1705,7 +1703,7 @@ module.exports = (function() {
           }
           peg$silentFails--;
           if (s5 === peg$FAILED) {
-            s4 = peg$c41;
+            s4 = peg$c39;
           } else {
             peg$currPos = s4;
             s4 = peg$c0;
@@ -1770,7 +1768,7 @@ module.exports = (function() {
         s5 = peg$parseLineTerminator();
         peg$silentFails--;
         if (s5 === peg$FAILED) {
-          s4 = peg$c41;
+          s4 = peg$c39;
         } else {
           peg$currPos = s4;
           s4 = peg$c0;
@@ -1796,7 +1794,7 @@ module.exports = (function() {
           s5 = peg$parseLineTerminator();
           peg$silentFails--;
           if (s5 === peg$FAILED) {
-            s4 = peg$c41;
+            s4 = peg$c39;
           } else {
             peg$currPos = s4;
             s4 = peg$c0;
@@ -1839,7 +1837,7 @@ module.exports = (function() {
       s2 = peg$parseReservedWord();
       peg$silentFails--;
       if (s2 === peg$FAILED) {
-        s1 = peg$c41;
+        s1 = peg$c39;
       } else {
         peg$currPos = s1;
         s1 = peg$c0;
@@ -2319,7 +2317,7 @@ module.exports = (function() {
       }
       peg$silentFails--;
       if (s2 === peg$FAILED) {
-        s1 = peg$c41;
+        s1 = peg$c39;
       } else {
         peg$currPos = s1;
         s1 = peg$c0;
@@ -2396,7 +2394,7 @@ module.exports = (function() {
       }
       peg$silentFails--;
       if (s2 === peg$FAILED) {
-        s1 = peg$c41;
+        s1 = peg$c39;
       } else {
         peg$currPos = s1;
         s1 = peg$c0;
@@ -2596,7 +2594,7 @@ module.exports = (function() {
       }
       peg$silentFails--;
       if (s2 === peg$FAILED) {
-        s1 = peg$c41;
+        s1 = peg$c39;
       } else {
         peg$currPos = s1;
         s1 = peg$c0;
@@ -2694,7 +2692,7 @@ module.exports = (function() {
           s3 = peg$parseDecimalDigit();
           peg$silentFails--;
           if (s3 === peg$FAILED) {
-            s2 = peg$c41;
+            s2 = peg$c39;
           } else {
             peg$currPos = s2;
             s2 = peg$c0;
@@ -2867,7 +2865,7 @@ module.exports = (function() {
       }
       peg$silentFails--;
       if (s2 === peg$FAILED) {
-        s1 = peg$c41;
+        s1 = peg$c39;
       } else {
         peg$currPos = s1;
         s1 = peg$c0;
@@ -3393,7 +3391,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3430,7 +3428,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3467,7 +3465,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3504,7 +3502,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3541,7 +3539,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3578,7 +3576,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3615,7 +3613,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3652,7 +3650,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3689,7 +3687,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3726,7 +3724,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3763,7 +3761,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3800,7 +3798,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3837,7 +3835,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3874,7 +3872,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3911,7 +3909,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3948,7 +3946,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -3985,7 +3983,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4022,7 +4020,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4059,7 +4057,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4096,7 +4094,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4133,7 +4131,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4170,7 +4168,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4207,7 +4205,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4244,7 +4242,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4281,7 +4279,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4318,7 +4316,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4355,7 +4353,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4392,7 +4390,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4429,7 +4427,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4466,7 +4464,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4503,7 +4501,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4540,7 +4538,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4577,7 +4575,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4614,7 +4612,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4651,7 +4649,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4688,7 +4686,7 @@ module.exports = (function() {
         s3 = peg$parseIdentifierPart();
         peg$silentFails--;
         if (s3 === peg$FAILED) {
-          s2 = peg$c41;
+          s2 = peg$c39;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
@@ -4837,7 +4835,7 @@ module.exports = (function() {
       }
       peg$silentFails--;
       if (s1 === peg$FAILED) {
-        s0 = peg$c41;
+        s0 = peg$c39;
       } else {
         peg$currPos = s0;
         s0 = peg$c0;
diff --git a/spec/parser.spec.js b/spec/parser.spec.js
index f484374..69bada4 100644
--- a/spec/parser.spec.js
+++ b/spec/parser.spec.js
@@ -294,12 +294,8 @@ describe("PEG.js grammar parser", function() {
   it("parses PrefixedExpression", function() {
     expect('start = $"abcd"?'   ).toParseAs(oneRuleGrammar(textOptionalLiteral));
     expect('start = $\n"abcd"?' ).toParseAs(oneRuleGrammar(textOptionalLiteral));
-    expect('start = &{ code }'  ).toParseAs(oneRuleGrammar(semanticAnd));
-    expect('start = &\n{ code }').toParseAs(oneRuleGrammar(semanticAnd));
     expect('start = &"abcd"?'   ).toParseAs(oneRuleGrammar(simpleAndOptionalLiteral));
     expect('start = &\n"abcd"?' ).toParseAs(oneRuleGrammar(simpleAndOptionalLiteral));
-    expect('start = !{ code }'  ).toParseAs(oneRuleGrammar(semanticNot));
-    expect('start = !\n{ code }').toParseAs(oneRuleGrammar(semanticNot));
     expect('start = !"abcd"?'   ).toParseAs(oneRuleGrammar(simpleNotOptionalLiteral));
     expect('start = !\n"abcd"?' ).toParseAs(oneRuleGrammar(simpleNotOptionalLiteral));
     expect('start = "abcd"?'    ).toParseAs(oneRuleGrammar(optionalLiteral));
@@ -322,6 +318,7 @@ describe("PEG.js grammar parser", function() {
     expect('start = [a-d]'     ).toParseAs(classGrammar([["a", "d"]], "[a-d]"));
     expect('start = .'         ).toParseAs(oneRuleGrammar({ type: "any" }));
     expect('start = a'         ).toParseAs(ruleRefGrammar("a"));
+    expect('start = &{ code }' ).toParseAs(oneRuleGrammar(semanticAnd));
     expect('start = ("abcd")'  ).toParseAs(literalGrammar("abcd"));
     expect('start = (\n"abcd")').toParseAs(literalGrammar("abcd"));
     expect('start = ("abcd"\n)').toParseAs(literalGrammar("abcd"));
@@ -332,6 +329,14 @@ describe("PEG.js grammar parser", function() {
     expect('start = a').toParseAs(ruleRefGrammar("a"));
   });
 
+  /* Canonical SemanticPredicateExpression is "\"abcd\"". */
+  it("parses SemanticPredicateExpression", function() {
+    expect('start = &{ code }'  ).toParseAs(oneRuleGrammar(semanticAnd));
+    expect('start = &\n{ code }').toParseAs(oneRuleGrammar(semanticAnd));
+    expect('start = !{ code }'  ).toParseAs(oneRuleGrammar(semanticNot));
+    expect('start = !\n{ code }').toParseAs(oneRuleGrammar(semanticNot));
+  });
+
   /* The SourceCharacter rule is not tested. */
 
   /* Canonical WhiteSpace is " ". */
diff --git a/src/parser.pegjs b/src/parser.pegjs
index 4eb872a..bd87c6c 100644
--- a/src/parser.pegjs
+++ b/src/parser.pegjs
@@ -107,24 +107,12 @@ PrefixedExpression
         expression: expression
       };
     }
-  / "&" __ code:CodeBlock {
-      return {
-        type: "semantic_and",
-        code: code
-      };
-    }
   / "&" __ expression:SuffixedExpression {
       return {
         type:       "simple_and",
         expression: expression
       };
     }
-  / "!" __ code:CodeBlock {
-      return {
-        type: "semantic_not",
-        code: code
-      };
-    }
   / "!" __ expression:SuffixedExpression {
       return {
         type:       "simple_not",
@@ -159,6 +147,7 @@ PrimaryExpression
   / CharacterClassMatcher
   / AnyMatcher
   / RuleReferenceExpression
+  / SemanticPredicateExpression
   / "(" __ expression:Expression __ ")" { return expression; }
 
 RuleReferenceExpression
@@ -166,6 +155,10 @@ RuleReferenceExpression
       return { type: "rule_ref", name: name }
     }
 
+SemanticPredicateExpression
+  = "&" __ code:CodeBlock { return { type: "semantic_and", code: code }; }
+  / "!" __ code:CodeBlock { return { type: "semantic_not", code: code }; }
+
 /* "Lexical" elements */
 
 SourceCharacter